牛客网 矩阵中的路径

题目：

解题：

public class Solution {
    public boolean hasPath(char[] matrix, int rows, int cols, char[] str) {
        int flag[] = new int[matrix.length];
        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < cols; j++) {
                if (helper(matrix, rows, cols, i, j, str, 0, flag))
                    return true;
            }
        }
        return false;
    }

    private boolean helper(char[] matrix, int rows, int cols, int i, int j, char[] str, int k, int[] flag) {
        int index = i * cols + j;//将矩阵行列的位置换算成下标
        if (i < 0 || i >= rows || j < 0 || j >= cols || matrix[index] != str[k] || flag[index] == 1)
            return false;
        if(k == str.length - 1) return true;//刚好匹配到最后一个字符
        flag[index] = 1;
        if (helper(matrix, rows, cols, i - 1, j, str, k + 1, flag)
                || helper(matrix, rows, cols, i + 1, j, str, k + 1, flag)
                || helper(matrix, rows, cols, i, j - 1, str, k + 1, flag)
                || helper(matrix, rows, cols, i, j + 1, str, k + 1, flag)) {
            return true;
        }
        flag[index] = 0;
        return false;
    }
}